Question

A group of atoms is confined to a very small (point-like) volume
ina laser-based atom trap. The incident laser light causes eachatom
to emit 1.7*106 photons of wavelength 610nm everysecond.
A sensor of area 1.8cm2 measures the lightintensity
emanating from the trap to be 4.6nW when placed 30cm awayfrom the
trapped atoms.

Assuming each atom emits photons with equal probability in
alldirections, determine the number of atoms trapped.